Sand starts by taking up a lot of pages to make the point that the concept of a 'nation' is primarily culturally defined. Beyond the tribe, or small village, the concept is abstract by design, so what's left is a sense of inclusion to a group of individuals who share a number of things in common.
Then, the 'nation-state' could only have come about in a post-agrarian society, one where a certain amount of social mobility, universal suffrage and access to education for all exists. This, because in the absence of these things, the community, or country if you will, can only exist as groups of individuals with varied ideas and customs, having very different visions and possibilities in life, even if they are ethnically similar.
This of course means that 'nation' has nothing to do with 'ethnicity', though the two obviously can overlap.
Sands underpins this with the claim that nationalism rests on two pillars, an inclusive and an exclusive one. Dutch, French or American nationalism are examples of nationalism resting stronger on the former, where, when immigrants adopt cultural practices and the language, they are quickly considered 'native', whereas eastern European forms of nationalism rest more on the latter, where ethnic composition is often of more importance.
Sands suggests that these different forms of nationalism, or rather, which one has the upper hand in any one country, derives from the social markup of the upper strata of society at, roughly, the start of the industrial revolution.
A country like Holland has always been very much ethnically mixed, with, specifically, an ethnically mixed layer the economically powerful, from the late middle ages onwards. In a situation like that, ethnicity is useless to shape a bond of nationhood, and only culture is left.
On the other hand, in many eastern European countries, it was the ethnically fairly uniform nobility which became the economically powerful. Then, using that ethnicity as a bond, it could also be used to protect this homogenous crowd from outside influences. Hence, this evolving into a form of nationalism which relies much more on ethnicity than it does on culture.
The second chapter of the book is a verbose piece to show that Jews only started seeing themselves as a homogenous nation towards the second half of the 19th century, this idea mainly developing in the new German state, when the stories of the old testament were starting to be taken more and more as literal truth.
With the Israeli distinction between Jewish and general history, this is persisting to this day, even though modern archeology belies both the validity and the supposed timeframe of the old testament, perhaps the stories related in the bible having only occurred, if at all, as late as the 5th century BC.
Sand continuous that no exile was forced upon the Jews after the second destruction of the temple, though to some extent the diaspora did increase in size. Though a lot of the expansion of the size of the number of Jews shortly after was primarily due to proselityzation, which makes sense considering the surprising rise in the number of Jews in the first few centuries after the supposed birth of Jesus.
More interesting, Sands shows that even the founders of the modern Jewish state believed that those living in Palestine were in fact ethnic brethren of the Jewish diaspora, who could be made part of the Jewish nation as equals. Clearly, though this is reasonable to assume from an ethnic perspective, both linguistically and culturally the Palestinians having clear links with the old Jewish inhabitants, or more accurately, their forefathers before they converted to Islam having had those links. They themselves having had slightly other ideas about the reintroduction of the Jewish faith into their lands.
Then, Sand describes a few kingdoms, roughly around the Mediteranean, which converted to Judaism, but were ethnically very different from the 'classical' Jews and on which Jewish historiographers have been surprisingly quiet. These include the Khazars in modern day Russia, the Himyar in Yemen and Berbers under queen Kahina on the southern shores of the Mediterranean. The Khazars, interestingly, are not unlikely the source of the vast majority of European jews, meaning that the vast majority of Jews 'returning' to Israel after the second world war never had forefathers who left the Mediterranean in the first place.
With the Zionist movement taking shape at the end of the 19th century, across a culturally diverse, and mostly eastern, Europe, there was no culture for the Zionists to shape bonds between the far flung Jewish communities. Jews of, say, Lithuania, being more like other Lithuanians than the Jews of, say, Greece, they in turn being more like their neighboring Greeks.
The only thing left was ethnicity, which fitted well with the emerging national movements in eastern Europe. However, because also ethnically the diversity was great, Zionist thinkers had to move back in time further, using the shared history as related in the old testament, of a wandering Jewish race, expelled or having left the promised land, as a grand unifier for the world's Jews and a justification for their return after the second world war. Never mind that Judaism largely spread through intermarriage and proselityzation, meaning that most Jews are in fact not at all descendent of the Jews who once left the eastern Mediterranean. And with Israel slowly changing into a proper ethnocacry, not only is the country an apartheid state, the irony is that the supposed Jewish nation doesn't exist but as a collection of believers.
Very readable and interesting, if a bit longwinded at times.